Normally, such transmission units include variable drives with continuously adjustable friction wheels that contain at least two toroidal disks and a toroidal running surface with rolls moving between the disks and running surface. Besides the continuously adjustable change in gears, variable drives with friction wheels exhibit a high torque capacity.
DE 196 29 213 A1 describes a transmission that can be operated in two different ranges of performance. The main components of these well-known friction wheel transmissions are a continuously adjustable variable drive with friction wheels and two paired interacting toroidal running surfaces, a secondary shaft, and an integrating transmission. Split power is provided for in the low cruising range (LOW). The drive power is conducted from the drive shaft through a transmission stage to the secondary shaft and on to the continuously adjustable transmission (variable drive with friction wheel). On the power take-off side, it is connected to the integrating transmission. A second power branch will conduct the drive power, via a secondary shaft, and a transmission stage directly into the integrating transmission. The power of both branches will then be combined and transferred to the output shaft.
In the second range of performance (HIGH) of this well-known transmission, the drive power will be transmitted through a transmission stage to the secondary shaft and subsequently to the continuously adjustable transmission. There is no additional power provided in this case.
Another transmission unit is described in the Applicant's DE 197 03 544 A1. It provides for split power and uses a continuously adjustable transmission unit, in particular a transmission unit consisting of interacting toroidal running surfaces (friction wheel transmission) paired together. This well-known transmission unit, too, includes an intermediate shaft and/or secondary shaft in order to achieve the desired split power.
A split power, dual area, transmission unit, as described above, is contained in EP 1 253 350 A2. To increase overall effectiveness, a gear is engaged in overdrive, because a variable drive, in general, shows less effectiveness than the application of a positive power or torque transmission device. Here, the transmission includes a double-tension, toroidal variable drive, an integrating transmission containing a planetary set and a planetary set used as a reverse transmission. All units are arranged in the direction of the power flow.
Furthermore, there is a transmission unit described in the Applicant's DE 100 43 623 A1. This unit consists of a drive shaft, at least one output shaft, and a configuration that allows for a change in the transmission ratio between the drive shaft and the output shaft by connecting the drive shaft with a startup unit that is connected to a continuously adjustable transmission. Furthermore, the continuously adjustable transmission is connected to a transfer gearbox, which contains a drive shaft for rear wheel drive operation and a second drive shaft for front wheel drive operation. Provisions can be made that the transmission unit is constructed as a two-zone transmission designed as a geared neutral transmission unit. In this well-known transmission, in order to shift to HIGH, the sun gear will interlock with the internal gear of an integrating transmission used as a planetary set which has the disadvantage of creating a high coupling torque.
The purpose of the present invention is to specify a split power transmission including a variable drive that will avoid high coupling torque in the upper cruising range. Furthermore, production of the invented transmission must be cost effective and utilize as little installation space as possible.